I used to swear all the time - it was horrible and made me sound like an idiot. There is nothing as ineloquent as a person whose every other word is a swearword (possibly a person whose every other word is 'like'). I don't think I ever made a conscious effort to quit, really - at some point I just realized "I'm over this" and I stopped. Of course, if someone is perfectly happy swearing, they should do so to their heart's content, but I understand why you would want to stop or cut down. Swearwords do lose their impact if you use them all the time.
Some things that may help:
- tell your friends that you're trying to quit swearing, and ask them to remind you every time you swear. It's hard to be conscious of one's own language at times and being reminded by others can be annoying in the short run (as in, when someone calls you out for the fifth time that sentence) but really helps to make you more aware of how you speak, and to find substitutes in your speech.
- if possible, get those around you to cut down as well - what helped me the most was probably that the people around me stopped swearing. (not because I told them to, just as a sort of common decision) I find I tend to adapt to the language that I hear, and pick up and drop words and ways of speech as they are used by those around me.
That's basically all the advice I can give. I'm trying to break my own habit of constantly using the Norwegian equivalents of "like" and "sort of" as filler words, and as you say it's really hard to break a speech pattern. Luckily, my father has decided to annoy me to death by asking "is it LIKE that, or is it that?" every time I slip up, so it's getting better.

(also, woo for using fantasy swearwords! I desperately want to start including Clockwork Orange words into my normal vocabulary.)